1. Field of the Invention
The present invention relates to an apparatus and a method of generating waveforms for driving a print head used for serial printers such as ink-jet printers and impact dot printers. Particularly, this invention relates to an apparatus and a method of generating driving waveforms for driving a print head, capable of programmably generating driving waveforms by retrieving driving waveforms per wave portion at a given timing from a memory, etc., in which the overall driving waveform data have been stored and converting the overall driving-waveform data into analog signals.
2. Related Background Art
Ink-jet printers have a print head with several nozzles in a sub-scanning (perpendicular) direction. The print head is moved in a main-scanning (horizontal) direction by a carriage mechanism while a paper is being fed, thus producing desired printouts.
The print head discharges ink drops through the nozzles at a given timing based on dot-pattern data developed from printing data entered by a host computer. The ink drops are sprayed onto a printing storage medium such as a printing paper.
Ink-jet printers, however, cannot produce printouts at an intermediate gradation such as gray due to the fact that they discharge ink drops or not, in other words, perform a dot-on/off control.
A known method of producing an intermediate gradation uses a dot matrix of 4xc3x974 or 8xc3x978 for one pixel. Another known technique for producing enhanced gradation is to discharge ink drops of various weights through the same nozzle per dot for dot control so that dots of various diameters are printed on a printing paper.
Variation in head-driving waveforms is required for discharging ink drops of various weights through the same nozzle. Such a known technique is described below.
FIG. 1 is a schematic illustration of an ink-jet printer hardware configuration.
An ink-jet printer 1 is equipped with a printing engine 3 for an actual printing operation and a printer controller 2 that controls the printing engine 3.
The printer controller 2 includes a CPU 24 for executing a control program, etc., stored in a ROM (Read Only Memory) 22, an EEPROM (Electrically Erasable and Programmable Read Only Memory) 21 that is a non-volatile memory for storing various setting-data, a RAM 23 acting as a main memory for the CPU 24 and also an image buffer memory for developing printing data into bit maps, and a custom-IC chip 25 such as an ASIC (Application-Specified Integrated Circuit).
All of these devices in the printer controller 2 are controlled by the CPU 24 via buses connected among the devices. The custom-IC chip 25 outputs signals for controlling several sections that constitute the printing engine 3. The IC chip 25 also acts as an interface for receiving print-command data entered from the host computer 5 via an interface port 4 under IEEE (Institute of Electrical and electronics Engineers)xe2x80x941284 standards.
The print engine 3 has a motor 31 for driving a carriage (not shown), a print head 32 mounted on the carriage, and a D/A (Digital-to-Analog)-converter IC chip 33 for applying analog driving-voltage waveforms to the print head 32.
A transfer line 27 is a bus line with a bit width corresponding to the number of nozzles mounted on the print head 32. An ink-discharging or -halting signal is sent to the print head 32 per nozzle along the transfer line 27 based on image buffer-data developed in the RAM 23 while a driving voltage to the print head 32 depends on an analog voltage waveform generated by the D/A-converter IC chip 33.
FIG. 2 is a graph showing an example of a head driving-voltage waveform in which the abscissa and the ordinate are time and voltage variation applied on a piezoelectric vibrator of the print head. Several trapezoidal waveform patters such as shown in FIG. 2 are prepared for discharging various sizes of ink drops. The trapezoidal waveform patters are combined for production of various sizes for ink drops.
Trapezoidal waveforms such as shown in FIG. 2 are formed in combination of directed segments. In detail, each of periods from moments T1 to T8 is expressed as vector data with gradient and length.
The known ink-jet printer forms these trapezoidal waveforms as follows.
The D/A-converter IC chip 33 has a memory that stores data in address spaces such as a Table 30 in FIG. 3. In the figure, 8-bit data is stored in each address space expressed by 5-bit data. Each 8-bit data is a value indicating a height in unit length of each directed segment, or segment gradient shown in FIG. 2. There are 32 different gradient values (for 5 bits) in FIG. 3 required for forming each segment of the trapezoidal waveform shown in FIG. 2.
In FIG. 1, in accordance with data on ink-drop sizes carried by a print command sent from the host computer 5, the custom-IC chip 25 designates a gradient address for forming each directed segment and sends the gradient address to the D/A-converter IC chip 33. The transfer line 26 for this data transfer is constituted by 5-bit address buses, clock signal lines for synchronous communications and data-latch signal lines.
Shown in FIG. 4 is a timing chart for each signal line of the transfer line 26 in data transfer. Data are latched at timing when they are fed on address-bus signal lines A0 to A4.
Height values (right column in Table 30) corresponding to the addresses are added by the number of clocks to obtain a height of one directed segment, as illustrated in FIG. 5. It is understood from FIG. 3 that accumulation of the height values (right column in Table 30) like steps by the number of clocks produces one directed segment. The larger the height value, the steeper the gradient whereas the smaller the value, the more gentle the gradient. A value accumulated by an adder is rounded to an appropriate number of bits and converted into an analog voltage based on the number of bits.
The driving-waveform generation described above is, however, restricted in the number of waveform gradients, and hence disadvantageous in generation of complex waveforms.
Formation of further multilevel dots has been studied for further multiple gradation. However, the known driving-waveform generation described above could not be adapted for such multilevel dots due to requirement of more complex driving waveforms.
The known method requires height values corresponding to various gradients of segments in the memory of the D/A-converter IC chip in formation of directed segments. The memory must have a very large storage capacity for generation of further various waveforms, thus resulting in cost-up.
In view of the problems discussed above, a purpose of the present invention is to provide an apparatus and a method of appropriately generating desired waveforms for driving an ink-jet print head with a simple configuration.
Another purpose of the present invention is to provide an apparatus and a method of generating several and complex waveforms for driving an ink-jet print head for multiple gradation.
In order to attain the purposes, in an apparatus and a method of generating several and complex waveforms for driving an ink-jet print head, waveform data for overall head-driving waveforms is written per given unit in waveform buffers and then sequentially retrieved at a given timing for analog conversion to obtain an analog head-driving waveform signal per given unit.
Therefore, features of a driving-waveform generating apparatus according to claim 1 are writing waveform data for overall head-driving waveforms per given unit in waveform buffers and sequentially retrieving the waveform data at a given timing for analog conversion to obtain an analog head-driving waveform signal per given unit.
Features of a driving-waveform generating apparatus according to claim 2 that is an apparatus for generating at least one assumed waveform for driving an ink-jet print head in accordance with gradation data are a waveform-data writing section for appropriately writing waveform data for overall head-driving waveforms, a waveform-data retrieving section for retrieving the waveform data written in the waveform-data writing section, a digital/analog converting section for converting the waveform data retrieved by the waveform-data retrieving section into an analog signal by digital/analog conversion, and a signal amplifying section for amplifying the analog signal output from the digital/analog conversing section.
A feature of a driving-waveform generating apparatus according to claim 3 is that the waveform-data writing section includes at least one waveform buffer in which the waveform data for the overall head-driving waveforms are temporarily written.
Features of a driving-waveform generating apparatus according to claim 4 are that the waveform-data writing section includes a waveform-buffer group having a plurality of waveform buffers, waveform data for overall various driving waveforms having been written in the waveform buffers, the waveform-data retrieving section selecting any one of the waveform buffers in the waveform-buffer group to retrieve the waveform data.
A feature of a driving-waveform generating apparatus according to claim 5 is that the waveform-buffer group has two waveform buffers, the waveform data being retrieved from one of the waveform buffers for generating waveform data for overall driving waveforms while the next waveform data is written in the other waveform buffer.
A feature of a driving-waveform generating apparatus according to claim 8 is a waveform-data storing section for storing at least one assumed driving-waveform data, data on several points forming a part of the assumed driving-waveform data being stored in the waveform-data storing section as a coordinate-data group.
A feature of a driving-waveform generating apparatus according to claim 9 is a waveform-data supplementation section for interpolating values between the points to the coordinate-data group, thus generating data on the overall driving waveforms.
Features of a driving-waveform generating apparatus according to claim 10 are that the waveform-buffer group has two waveform buffers, the waveform data being retrieved from one of the waveform buffers while the waveform-data supplementation section is interpolating the values between the points to the coordinate-data group, thus generating data on the overall driving waveform and the data on the overall driving waveforms is written in the other waveform buffer.
A feature of a driving-waveform generating apparatus according to claim 17 is that written in the one waveform buffer is a print head-control signal other than the driving waveforms in addition to the waveform data for overall head-driving waveforms, the control signal being retrieved by the waveform-data retrieving section and being applied to the print head.
Features of a driving-waveform generating apparatus according to claim 18 are that the waveform data for overall driving waveforms is converted into an analog signal by the digital/analog converting section and the analog signal is amplified by the signal amplifier, thus being output to the print head whereas the print head-control signal other than the driving waveform is output to the print head as it is as a digital signal.
A feature of a driving-waveform generating apparatus according to claim 19 is that the one waveform buffer has a storage capacity of 16 bits in a longitudinal direction and a given number of bits in a horizontal direction, the waveform data for overall driving waveforms being written on upper 10 bits among the 16 bits in the longitudinal direction, the print head-control signal other than the driving waveforms being written in lower 6 bits among the 16 bits in the longitudinal direction.
A feature of a driving-waveform generating apparatus according to claim 20 is that the print head-control signal other than the driving waveforms includes a waveform completion signal indicating completion of the waveforms, the least significant bit of the 16 bits in the longitudinal direction being used as an end bit in which the waveform completion signal is written.
A feature of a driving-waveform generating apparatus according to claim 21 is that when the waveform completion signal is detected in the end bit and when a certain storage capacity remains in the one waveform buffer, waveform data of other driving waveforms are written in the one waveform buffer.